All immune responses depend on antigens stimulating specific lymphocyte cells to become activated. This process involves a small, non-dividing cell enlarging, dividing several times, and building a secretory factory in the cytoplasm. For the B lymphocyte, the secreted product is an antibody. for an immune response to be appropriate to the stimulus, be this an infection or a vaccination, every step in this elaborate activation pathway needs to be controlled or fine-tuned. Our research aims to dissect the steps of activation and thus to understand the cellular mechanisms underlying antibody formation. This understanding will help the design of new and improved vaccines, and will allow deeper insights into autoimmune diseases. B lymphocytes will be obtained from the spleens and other lymphoid organs of mice. They will be fractionated by procedures that allow the isolation of cells predestined to form antibody only to a particular antigen of choice. Through microculture techniques, these antigen-specific B cells will be cultured as single cells over a 5 to 6-day period. They will be stimulated by controlled amounts of the antigen with which they are reactive, aided by one or more pure growth factors called interleukins or IL. Specifically, IL-4, IL-5, IL-6, IL-1 and IL-2 will be used both as single agents and in various permutations and combinations. Activation of single small B cells will be monitored microscopically through measured enlargement. Division will be noted through repeated microscopy. Antibody formation will be studied by assay of the microculture fluid, both for amount and for chemical kind or isotype". The project will have 4 linked aims. First, we shall establish exactly which phase of the activation cascade is controlled by which interleukin. Secondly, we will study mice that have been "tricked" into treating the foreign antigen as though it were part of the body itself (i.e. rendered immunologically tolerant) in the hope of defining more precisely the cellular mechanisms for self- recognition. Thirdly, we will examine different varieties (subsets) of B lymphocytes to see how and why they respond differentially to activation signals. Fourthly, we will investigate the regulated appearance and disappearance of specific protein receptors at the B cell surface for the various interleukins that control their growth and development.